Tooth whitening: concepts and controversies

Layout 1Introduction The cosmetic impairment of tooth discolouration, especially
in the anterior region, can be treated by a number of
invasive therapies such as indirect crowns and veneers,
microabrasion, or by the placement of direct composite. In
certain clinical situations, the procedure of tooth whitening
or bleaching can be employed as a less invasive alternative
to restoration with either ceramic or composite. Bleaching
of teeth can be achieved either by an external – or vital –
approach (nightguard vital bleaching) (Heywood 1991),
where vital teeth are bleached by direct contact with an
agent such as carbamine peroxide, or by an internal – or
non-vital – approach, where non-vital teeth are bleached
with an agent such as sodium perborate in a walking
bleach technique (Attin et al 2003). A third approach,
which is a modification of both techniques, can be
employed when bleaching vital and non-vital teeth in the
same arch. This is called inside/outside bleaching
(Settembrini et al 1997). The aim of this review is to discuss
the concepts involved in both the vital and non-vital
bleaching of teeth, and to provide advice, based on the
evidence from current literature, to reduce the risks of
complications and to ensure successful bleaching therapy.
Causes of tooth discolouration Tooth discolouration may be described as intrinsic, extrinsic
or a combination of both (Hattab et al 1999). It varies in
appearance, aetiology, severity, localisation and adherence
to tooth structure (Dahl and Pallesen 2003). The causes of
Tooth whitening: concepts and controversies
Johnny Fearon
Abstract Today’s society dictates that it is the norm for people to have straight, white teeth. The demand therefore for tooth
whitening in dental practice has increased exponentially over the last decade. A common approach to achieving this goal
is by bleaching. This article discusses clinical aspects of dental bleaching by providing an evidence-based review of current
literature. Topics covered include aetiology of tooth discolouration, indications for bleaching, its mode of action, and
different types of bleaching regimes, indications and potential side effects.
24 INTERNATIONAL DENTISTRY SA VOL. 11, NO. 2
Clinical
intrinsic tooth discolouration can be attributed to changes
to the structure of dentine or enamel (Figure 1), or by
incorporation of chromatogenic material into tooth tissue,
either during odontogenesis or post eruption. The main
cellular changes observed in intrinsically stained teeth often
provide a clue to the aetiology of the pathologic process
involved. Discolouration can manifest as either a red,
brown, grey or yellow appearance. Internal pulp bleeding
caused by trauma or pulp extirpation can cause a
temporary red colour change to the crown.
Then, as blood degenerates and breaks down, products
such as haemosiderin, haemin, haematin and haematoidin
release iron (Dahl and Pallesen 2003). The iron can be
converted into black ferric sulphide with hydrogen sulphide
produced by bacteria, which causes a grey staining of the
tooth. In addition to blood degradation, degrading proteins
of necrotic pulp tissue may also cause discolouration. If pulp
tissue is not completely extirpated and remains in the pulp
horns, discolouration may result from the break up of the
proteins of the necrotic pulp tissue (Guldener and Langeland
1993), causing a grey or brown hue to the crown (Figure 2).
Yellow discolouration is often due to the reactionary laying
down of tertiary dentine sclerosing the root canal and pulp
chamber. Because enamel is relatively translucent, the
additional volume of dentine obliterating the pulp chamber
produces a yellow hue to the crown (Figure 3) (Faunce 1983).
Intrinsic discolouration is also caused by exposure to high
levels of fluoride, tetracycline administration during
childhood, inherited developmental disorders, jaundice in
childhood, porphyria, caries, restorations and trauma to the
developing tooth germ. After eruption, ageing, pulp necrosis
INTERNATIONAL DENTISTRY SA VOL. 11, NO. 2 25
Clinical
discolouration (Olgart and Bergenholtz 2003). Extrinsic
staining results mainly from dietary factors and smoking
(Figure 4). Foods containing tannins such as red wine, coffee
and tea can give rise to extrinsic stain. Carotenes in oranges
and carrots, and tobacco use, whether it is smoking or
chewing, also give rise to extrinsic stain (Watts and Addy
2001). Wear of tooth structure, deposition of secondary
dentine due to ageing or as a consequence of pulp
inflammation, and dentine sclerosis affect the light-
transmitting properties of enamel and dentine, resulting in a
gradual discolouration. For example, tetracycline staining is
persistent, whereas discolouration of ageing responds
quickly in most instances (Heywood 1995).
History The first publications describing techniques and chemicals
for bleaching non-vital teeth appeared in the latter half of
the 19th Century. The bleaching agent of choice was
chloride of lime (Dwinelle 1850). Other agents described
for the bleaching of pulpless teeth included aluminium
chloride and hydrogen peroxide, used either alone or in
combination with heat. The active ingredient common to
all the early medicaments was an oxidising agent, which
acted either directly or indirectly with the organic
component of the tooth. Concern about the side effects
of some of these agents was justified however, because
some chemicals used were very poisonous, such as
cyanide of potassium (Barker 1861). The walking bleach
technique that was introduced in 1961 involved
placement of a mixture of sodium perborate and water
into the pulp chamber, which was sealed into place
between dental visits (Spasser 1961). This method was
later modified by replacing water with 30-35% hydrogen
peroxide to improve the whitening effect (Nutting 1963).
Although most of the early publications described non-
vital bleaching, a 3% solution of Pyrozone was used
safely as a mouthwash as early as 1890, which not only
Figure 1: Intrinsic tooth colour change due to tetracycline staining. Figure 2: Brown/grey appearance of a nonvital central incisor.
Figure 3: Yellow intrinsic discolouration of the upper right central incisor due to sclerosis of the pulp chamber.
Figure 4: Yellow discolouration of the maxillary anterior dentition due to extrinsic agents such as food colouring and tobacco use.
reduced caries, but also whitened teeth (Atkinson 1893).
The observation that carbamine peroxide caused
lightening of teeth was made in the late 1960s by an
orthodontist (Klusmier), who had prescribed an antiseptic
containing 10% carbamine peroxide to be used in a tray
for the treatment of gingivitis. This technique, which is
the method of home bleaching today, was not widely
accepted by the dental profession until 20 years later
when it was described in a 1989 publication (Haywood
and Heymann 1989).
Mechanism Hydrogen peroxide is a colourless liquid with a bitter taste
and is highly soluble in water to give an acid solution. It
has a wide number of industrial applications, for example
bleaching or deodorising textiles, wood pulp, fur and hair,
and in the treatment of water and sewage. Hydrogen
peroxide is a reactive oxygen species and acts as a strong
oxidising agent through the formation of free radicals
Tredwin et al 2006), which attack the organic molecules
responsible for tooth discolouration. When complex,
pigmented organic molecules (chromaphores) are broken
down by the action of free radicals, simpler molecules are
produced, which reflect less light (Frysh 1995). During
tooth bleaching, more highly pigmented carbon ring
compounds are converted to carbon chains, which are
lighter in colour. The carbon double bond chains (yellow in
colour) are converted into hydroxyl groups, which are
essentially colourless. The radicals also reduce coloured
metallic oxides like Fe2O3 (Fe3+) to colourless FeO (Fe2+).
The bleaching process continues until all of the original
pigment is rendered colourless (Albers 1991). The chemistry
of carbamine peroxide, used for nightguard vital bleaching,
is slightly different from hydrogen peroxide as it also
contains urea, which permits the peroxide to remain in
contact with the tooth for longer. Although the action of
carbamine peroxide also causes the breakdown of
pigmented carbon compounds as described above, the
degradation is slower than with hydrogen peroxide alone.
External (vital) bleaching The bleaching of vital teeth can occur inside the surgery
(power bleaching) or outside the surgery (nightguard vital
bleaching). Power bleaching accomplishes complete
lightening during treatment in the surgery, whereas
nightguard vital bleaching involves the application of a
peroxide gel to the tooth surface via some means of carrier,
usually a custom fitting bleaching tray.
Power bleaching Power bleaching of vital teeth generally uses a high
concentration of peroxide solution (35- 50% hydrogen
peroxide) placed directly on the teeth, often supplemented
by a heat or light source to activate or enhance peroxide
release (Feinman et al 1987). Because the hydrogen
peroxide concentration is so high, soft tissues must be very
well protected to prevent injury (Figure 5). Definite
indications for its use include treatment of generalised
gross staining such as tetracycline staining and perhaps
dentine sclerosis, which take a long time using the
nightguard vital bleaching technique, and for patients who
may have difficulty in compliance with the nightguard vital
bleaching technique.
1. Neither the patient nor the dentist can exactly control
the amount of lightening (compared to the nightguard vital
bleaching technique). The technique runs the risk of both
over- and under-bleaching.
2. The fee is usually higher as a greater amount of chair
time is required.
3. There is a possibility of soft tissue damage due to the
caustic nature of the high concentrations of peroxide.
4. There is a greater risk of post-operative sensitivity
(Goldstein 1988). A higher incidence of tooth sensitivity
(67-78%) was reported after power bleaching (Heywood
and Berry 2001, Cohen and Chase 1979) compared with
the nightguard vital bleaching method, using 10%
carbamine peroxide (15-65%) (Nathanson and Parra 1987,
Heywood 1996, Leonard 1998, Schulte et al 1994).
Nightguard vital bleaching Nightguard vital bleaching, or ‘take home’ bleaching, is the
more commonly used bleaching technique because it is
easy to perform and is generally less expensive for the
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Figure 5: A white silicone barrier material is used to protect the gingival tissues during power bleaching.
patient. It involves the use of a 10-20% solution of
carbamine peroxide in a gel form (approximately equal to
3.4-7% hydrogen peroxide) delivered to the tooth surface
by a custom-made, vacuum formed, plastic bleaching tray
(Figures 6 and 7). Manufacturers have offered carbamine
peroxide in a variety of different concentrations, ranging
from 10% to over 20%, but the best combination of
safety, limited side effects and speed of action is obtained
with a 10% solution of carbamine peroxide approved by
the ADA (American Dental Association). Products carrying
the ADA accepted label have passed a rigorous set of safety
and efficacy standards (Tam 1999). A survey by Christensen
(1989) indicated that 90% of dentists surveyed used a
10% concentration of carbamine peroxide for take home
bleaching (Christensen 1991). Although the evidence base
in the dental literature on the efficacy of nightguard vital
bleaching is mostly limited to case reports, it is generally
advocated that most teeth are susceptible to bleaching
(Tam 1999). The process requires longer contact time
compared to power bleaching, but it is safe and the results
are generally excellent (Figure 2). The first subjective
change in tooth colour is generally observed after two to
four sessions of bleaching. In a clinical study of nightguard
vital bleaching with 10% carbamine peroxide, 92% of
subjects experienced some lightening of teeth after a six-
week period (Haywood et al 1994). Another clinical trial by
Swift et al (1999) examined the efficacy of 10% carbamine
peroxide nightly for two weeks. They reported that the
lightness of the crown of the tooth increased by, on
average, eight shade units on the Vita¨ shade guide,
calibrated according to a lightness value.
Internal (non-vital) bleaching The whitening of endodontically treated teeth can be
carried out by an internal whitening treatment known as
non-vital bleaching or the ‘walking bleach technique’. This
therapy involves placement of a bleaching agent into the
empty pulp chamber of a non-vital, discoloured tooth, and
is a more conservative option compared to restoration with
veneers or crowns. The two most common bleaching
agents used for this technique are hydrogen peroxide and
sodium perborate, and various sources have been applied
to speed up the reaction and improve the bleaching effect.
The decomposition of hydrogen peroxide into active
oxygen is accelerated by application of heat or light (Howell
1980). The thermocatalytic breakdown of hydrogen
peroxide was proposed for many years as the best
technique for the whitening of non-vital, discoloured teeth
because of the high reactivity of hydrogen peroxide upon
application of heat (Hardman et al 1985). In this procedure,
heat from a special lamp or hot instrument was applied to
a well of 30-35% hydrogen peroxide in an empty pulp
chamber. Temporary restorations impregnated with 30-
35% hydrogen peroxide were often used between visits.
Although there is little doubt regarding the clinical efficacy
of non-vital bleaching using 30-35% hydrogen peroxide
(Chen et al 1993) (either thermoactivated or not), serious
concerns regarding the safety of this technique, in
particular the risk of producing external cervical root
resorption, which is discussed later, have rendered this
technique unadvisable, and the application of sodium
perborate instead of hydrogen peroxide is now
recommended. Sodium perborate is a hydrogen peroxide
releasing agent, and since 1907 it has been employed as an
oxidiser and bleaching agent, especially in washing
powders and other detergents. It comes in powder form
and can be mixed into a paste or putty with either pure
water or hydrogen peroxide. Several studies have reported
bleaching effectiveness by comparing mixtures of sodium
perborate with distilled water or hydrogen peroxide in
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Figure 6: Take-home bleaching tray, extended as far as the gingival margin.
Figure 7: Take-home bleaching tray in situ.
different concentrations. Rotstein et al (1991, 1993) and
Weiger et al (1994) did not report any significant difference
in effectiveness between sodium perborate mixed with 3-
30% hydrogen peroxide, and distilled water, except for the
time taken to achieve a clinically acceptable result.
However, mixing sodium perborate with hydrogen peroxide
was shown to accelerate the rate of colour change. In the
case of severe discolouration, it is safe to mix sodium
perborate with a 3% solution of hydrogen peroxide;
however it is not appropriate to use 30% hydrogen
peroxide because of the possible risk of inducing cervical
root resorption (Friedman et al 1988). This is discussed in
more detail below.
Clinical stages for internal bleaching 1. Radiographic examination A recent pre-operative
radiograph is necessary prior to treatment to assess the
quality of the root canal treatment. The root canal should
be thoroughly condensed along its whole length to prevent
the apico-coronal migration of micro-organisms or
bleaching agents, which may have a detrimental effect on
the surrounding tissues. Should the quality of the root
canal treatment be suboptimal, the tooth should undergo
corrective endodontic therapy prior to the commencement
of bleaching (Figure 8).
2. Preparation of the access cavity - The pulp space should
be completely debrided of any necrotic material, pulp
tissues, or restorative or root canal materials. The smear
layer on the dentinal surface of the pulp chamber is
removed by applying 37% phosphoric acid gel and
irrigated with 2.5-5% sodium hypochlorite.
3. Cervical seal - Gutta-percha (GP) is removed with a
round ended, long shank bur to a level of 1-2mm below
the CEJ (cementoenamel junction). It is helpful to measure
this distance pre-operatively by recording the distance from
the incisal tip to the CEJ on the facial aspect with a
graduated probe (Figures 9 and 10). The coronal access is
then sealed with a glass ionomer cement (GIC) or
accelerated zinc oxide (ZOE) plug to prevent the diffusion
of bleaching agents from the pulp chamber throughout
the root filling, as root fillings do not provide an effective
barrier on their own (Figure 11) (Attin et al 2003). Rotstein
et al (1992) demonstrated that a 2mm layer of GIC or
composite is essential. Alternatively, Bergenholtz et al
(1982) showed histologically that ZOE cement also provides
a hermetic seal.
4. Application of bleaching agent - A small drop of distilled
water is mixed with sodium perborate powder (Amosan¨
Oral-B) until a putty consistency is achieved (Figure 12). The
sodium perborate putty is applied to the empty pulp
chamber with an amalgam plugger or similar instrument,
covered with cotton pellet and sealed with an adhesive
provisional restoration. It is often difficult to place the
provisional restoration directly over the cotton pellet
without displacing it. To immobilise the pellet, it is helpful
to first wet the pellet with a bonding agent and then light
cure the bond once the pellet is in place. A provisional
restoration must then be placed, as a sound seal is required
around the access cavity to prevent leakage of the
bleaching agent into the oral cavity. A light cured GIC or an
accelerated ZOE material can be employed for this purpose.
This procedure is repeated every three to four days until
successful bleaching becomes apparent. This normally
occurs after one to four visits (Figure 13).
5. Permanent restoration - Once the desired colour change
has been achieved, a sound restoration with sealed
dentinal tubules is a prerequisite to a successful bleaching
therapy (Abou Raas 1998). The access cavity should be
restored with a composite, which is adhesively attached to
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Figure 8: The distance between the CEJ and the incisal edge is measured with a periodontal probe on the facial.
Figure 9: Having recorded the measurement between the CEJ and the incisal edge, the periodontal probe now assists in accurate.
Figure 10: Good quality root canal treatments, showing thorough obturation and access cavities prepared for internal bleaching.
both enamel and dentine. It is recommended to choose a
composite with a high value (light colour) to help
compensate if the bleaching therapy alone does not
provide the full extent of desired lightness. The timing of
placement of the final restoration is also important, as it
has been shown that the bond strengths of composite to
bleached enamel and dentine is temporarily reduced. It is
recommended to wait for at least seven days post
bleaching prior to bonding composite as a definitive
restoration (Nathanson and Parra 1987).
Inside/outside bleaching Another bleaching technique has been described for clinical
situations where an endodontically treated tooth is present
within the arch and the arch as a whole is to be bleached.
This technique, called ‘inside/outside bleaching’ allows the
endodontically treated tooth to be bleached both from
within the sealed pulp chamber (inside) and from the facial
enamel (outside) simultaneously. The technique for
inside/outside bleaching involves the fabrication of a
vacuum-processed plastic mouthguard, trimmed to the
facial and lingual margins as previously described for
nightguard vital bleaching. Coronal access to the
endodontically treated tooth (or teeth) is achieved and the
coronal GP is sealed with a light cured GIC or accelerated
ZOE, as previously described for non-vital bleaching. The
patient is instructed how to inject 10% carbamine peroxide
gel into the coronal orifice and into the nightguard. The
bleach tray is worn for a minimum of two hours, up to a
maximum of an overnight period, as described above. The
patient is then instructed to insert a cotton wool plug into
the coronal access to prevent the ingress of food particles.
Once the non-vital tooth has been bleached to an
acceptable match with the adjacent teeth, coronal access
can be definitively restored with a high-value shade
composite resin, and further nightguard vital bleaching can
be continued if desired (Settembrini et al 1997).
Controversies Tooth sensitivity Unfortunately the aetiology of bleaching-related tooth
sensitivity is neither well understood nor easily measured;
however the hydrodynamic theory is a mechanism
frequently cited to explain it (Brannstrom 1986). According
to this model, peroxide solutions introduced into the oral
environment contact available dentinal surfaces and cause
retraction of odontoblastic processes, resulting in rapid
fluid movement inside the dentinal tubules.…